#include <linux/mm.h>
  #include <linux/highmem.h>
  #include <linux/sched.h>

  #include <linux/hugetlb.h>

  
  static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pte_t *pte;
  	int err = 0;
  
  	pte = pte_offset_map(pmd, addr);

  	for (;;) {

  		err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);

  		if (err)
  		       break;

  		addr += PAGE_SIZE;
  		if (addr == end)
  			break;
  		pte++;
  	}

  
  	pte_unmap(pte);
  	return err;
  }
  
  static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pmd_t *pmd;
  	unsigned long next;
  	int err = 0;
  
  	pmd = pmd_offset(pud, addr);
  	do {

  again:

  		next = pmd_addr_end(addr, end);

  		if (pmd_none(*pmd)) {

  			if (walk->pte_hole)

  				err = walk->pte_hole(addr, next, walk);

  			if (err)
  				break;
  			continue;
  		}

  		/*
  		 * This implies that each ->pmd_entry() handler
  		 * needs to know about pmd_trans_huge() pmds
  		 */

  		if (walk->pmd_entry)

  			err = walk->pmd_entry(pmd, addr, next, walk);

  		if (err)
  			break;
  
  		/*
  		 * Check this here so we only break down trans_huge
  		 * pages when we _need_ to
  		 */
  		if (!walk->pte_entry)
  			continue;
  
  		split_huge_page_pmd(walk->mm, pmd);
  		if (pmd_none_or_clear_bad(pmd))
  			goto again;
  		err = walk_pte_range(pmd, addr, next, walk);

  		if (err)
  			break;
  	} while (pmd++, addr = next, addr != end);
  
  	return err;
  }
  
  static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pud_t *pud;
  	unsigned long next;
  	int err = 0;
  
  	pud = pud_offset(pgd, addr);
  	do {
  		next = pud_addr_end(addr, end);
  		if (pud_none_or_clear_bad(pud)) {
  			if (walk->pte_hole)

  				err = walk->pte_hole(addr, next, walk);

  			if (err)
  				break;
  			continue;
  		}
  		if (walk->pud_entry)

  			err = walk->pud_entry(pud, addr, next, walk);

  		if (!err && (walk->pmd_entry || walk->pte_entry))

  			err = walk_pmd_range(pud, addr, next, walk);

  		if (err)
  			break;
  	} while (pud++, addr = next, addr != end);
  
  	return err;
  }

  #ifdef CONFIG_HUGETLB_PAGE
  static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
  				       unsigned long end)
  {
  	unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
  	return boundary < end ? boundary : end;
  }
  
  static int walk_hugetlb_range(struct vm_area_struct *vma,
  			      unsigned long addr, unsigned long end,
  			      struct mm_walk *walk)
  {
  	struct hstate *h = hstate_vma(vma);
  	unsigned long next;
  	unsigned long hmask = huge_page_mask(h);
  	pte_t *pte;
  	int err = 0;
  
  	do {
  		next = hugetlb_entry_end(h, addr, end);
  		pte = huge_pte_offset(walk->mm, addr & hmask);
  		if (pte && walk->hugetlb_entry)
  			err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
  		if (err)
  			return err;
  	} while (addr = next, addr != end);
  
  	return 0;
  }

  
  static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)
  {
  	struct vm_area_struct *vma;
  
  	/* We don't need vma lookup at all. */
  	if (!walk->hugetlb_entry)
  		return NULL;
  
  	VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
  	vma = find_vma(walk->mm, addr);
  	if (vma && vma->vm_start <= addr && is_vm_hugetlb_page(vma))
  		return vma;
  
  	return NULL;
  }
  
  #else /* CONFIG_HUGETLB_PAGE */
  static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)
  {
  	return NULL;
  }
  
  static int walk_hugetlb_range(struct vm_area_struct *vma,
  			      unsigned long addr, unsigned long end,
  			      struct mm_walk *walk)
  {
  	return 0;
  }
  
  #endif /* CONFIG_HUGETLB_PAGE */

  /**
   * walk_page_range - walk a memory map's page tables with a callback

   * @mm: memory map to walk
   * @addr: starting address
   * @end: ending address
   * @walk: set of callbacks to invoke for each level of the tree

   *
   * Recursively walk the page table for the memory area in a VMA,
   * calling supplied callbacks. Callbacks are called in-order (first
   * PGD, first PUD, first PMD, first PTE, second PTE... second PMD,
   * etc.). If lower-level callbacks are omitted, walking depth is reduced.
   *

   * Each callback receives an entry pointer and the start and end of the
   * associated range, and a copy of the original mm_walk for access to
   * the ->private or ->mm fields.

   *

   * Usually no locks are taken, but splitting transparent huge page may
   * take page table lock. And the bottom level iterator will map PTE

   * directories from highmem if necessary.
   *
   * If any callback returns a non-zero value, the walk is aborted and
   * the return value is propagated back to the caller. Otherwise 0 is returned.

   *
   * walk->mm->mmap_sem must be held for at least read if walk->hugetlb_entry
   * is !NULL.

   */

  int walk_page_range(unsigned long addr, unsigned long end,
  		    struct mm_walk *walk)

  {
  	pgd_t *pgd;
  	unsigned long next;
  	int err = 0;
  
  	if (addr >= end)
  		return err;

  	if (!walk->mm)
  		return -EINVAL;
  
  	pgd = pgd_offset(walk->mm, addr);

  	do {

  		struct vm_area_struct *vma;

  		next = pgd_addr_end(addr, end);

  		/*
  		 * handle hugetlb vma individually because pagetable walk for
  		 * the hugetlb page is dependent on the architecture and
  		 * we can't handled it in the same manner as non-huge pages.
  		 */

  		vma = hugetlb_vma(addr, walk);
  		if (vma) {

  			if (vma->vm_end < next)
  				next = vma->vm_end;

  			/*
  			 * Hugepage is very tightly coupled with vma, so
  			 * walk through hugetlb entries within a given vma.
  			 */
  			err = walk_hugetlb_range(vma, addr, next, walk);

  			if (err)
  				break;

  			pgd = pgd_offset(walk->mm, next);

  			continue;
  		}

  		if (pgd_none_or_clear_bad(pgd)) {
  			if (walk->pte_hole)

  				err = walk->pte_hole(addr, next, walk);

  			if (err)
  				break;

  			pgd++;

  			continue;
  		}
  		if (walk->pgd_entry)

  			err = walk->pgd_entry(pgd, addr, next, walk);

  		if (!err &&
  		    (walk->pud_entry || walk->pmd_entry || walk->pte_entry))

  			err = walk_pud_range(pgd, addr, next, walk);

  		if (err)
  			break;

  		pgd++;
  	} while (addr = next, addr != end);

  
  	return err;
  }